1. Field of Industrial Utilization
This invention relates to a magnetic recording medium and more particularly, it relates to a magnetic recording medium which shows a high output in a broad range of recording density.
2. Discussion of Related Art
The increasing demand for high-density recording has prompted the research into various new recording systems. Especially in the field of magnetic recording, the vertical magnetic recording system is deemed as one of the most promising high-density recording methods and enthusiastic studies are being made on this system. As the material of recording media used for such vertical magnetic recording, there have been proposed Co--Cr alloy film, which is most highly prized, Co--O film, Fe--M--O films (M representing Sn, Ge, etc.), and the films in which Fe or other elements have been electrodeposited in fine pores of anodized aluminum, and the results of many tests and experiments have verified their excellent high-density recording performance.
The vertical recording system using such magnetic media is indeed excellent in high-density recording characteristics as mentioned above, but on the other hand this system has the problem that it is low in low-density recording output as compared with the conventional longitudinal recording system.
This is attributable to the fact that a strong demagnetizing field is generated by the free magnetic pole formed on the rear side of the film when the vertical recording medium is magnetized, and such strong demagnetizing field acts to attenuate recording magnetization. Therefore, it should be an effective measure against such a problem to interpose a soft magnetic layer between the vertical magnetized recording layer and the substrate so as to reduce the activity of the free magnetic pole at the interface adjoining the soft magnetic layer. This concept has already been disclosed in U.S. Pat. No. 4,210,946, and further studies are being made on this double-layer film recording medium.
This type of recording medium, however, has had some difficult problems. Firstly, when a vertical magnetically anisotropic recording layer, such as a Co--Cr film, is formed on the soft magnetic layer, such as a permalloy layer, the crystal orientation of the Co--Cr film would be disturbed. Secondly, as disclosed by Uesaka et al in Journal of Applied Physics, 57, 3925 (1985), spike noise is produced in the soft magnetic layer to make it unable to obtain a good S/N ratio. Thirdly, in case the double-layer film recording medium is used in combination with a ring head, the head magnetic field in the vertical direction becomes broad due to the presence of the soft magnetic layer, resulting in the deteriorated high-density recording performance.